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United States Patent |
5,567,579
|
Gourlaouen
,   et al.
|
October 22, 1996
|
Photographic product comprising a blend of emulsions with different
sensitivities
Abstract
The present invention concerns a photographic product containing at least
one light-sensitive layer consisting of a blend of silver halide
emulsions.
The blend of the invention is formed by at least one pure bromide emulsion,
the proportion of fast emulsion grains in the blend is less than 50%
compared with the total number of silver halide grains, and the proportion
of slow emulsion grains in the blend is greater than 20%.
The present invention makes it possible to obtain a radiation-sensitive
photographic product which has improved sensitivity and granularity.
Inventors:
|
Gourlaouen; Luc R. (Givry, FR);
Friour; Gerard A. D. (Chalon-sur Saone, FR);
Martin; Didier J. (Givry, FR);
Strauel; Philippe (Givry, FR)
|
Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
Appl. No.:
|
431393 |
Filed:
|
April 28, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
430/567; 430/495.1; 430/564 |
Intern'l Class: |
G03C 001/005; G03C 001/494 |
Field of Search: |
430/495,564,567,379
|
References Cited
U.S. Patent Documents
3737317 | Jun., 1973 | Nicholas et al. | 430/505.
|
3923515 | Dec., 1975 | van Stappen | 430/396.
|
3942986 | Mar., 1976 | Florens | 430/567.
|
3989527 | Nov., 1976 | Locker | 430/567.
|
4446228 | May., 1984 | Honda et al. | 430/567.
|
4599302 | Jul., 1986 | Scheerer | 430/509.
|
4617259 | Oct., 1986 | Ogawa et al. | 430/509.
|
4639410 | Jan., 1987 | Mochizuki et al. | 430/567.
|
4656122 | Apr., 1987 | Sowinski et al. | 430/505.
|
4672026 | Jun., 1987 | Daubendiek | 430/567.
|
4689292 | Aug., 1987 | Metoki et al. | 430/567.
|
4755449 | Jul., 1988 | Inoue et al. | 430/267.
|
4865964 | Sep., 1989 | Newmiller | 430/569.
|
4917996 | Apr., 1990 | Matsuzaka et al. | 430/569.
|
Foreign Patent Documents |
0083239 | Dec., 1982 | EP.
| |
0063962 | Jan., 1987 | EP.
| |
63-259650 | Oct., 1988 | JP.
| |
Primary Examiner: Letscher; Geraldine
Attorney, Agent or Firm: Leipold; Paul A.
Parent Case Text
This is a continuation of application Ser. No. 08/213,320 filed Mar. 15,
1994, now abandoned.
Claims
We claim:
1. A reversal photographic product comprising at least one light sensitive
silver halide emulsion layer consisting of a blend of monodisperse silver
halide emulsions comprising at least one each of a fast silver halide
emulsion and one slow silver halide emulsion, and optionally comprising a
medium silver halide emulsion characterized in that
1) at least one of the emulsions making up the blend is a pure bromide
emulsion and at least one of the emulsions making up the blend is a
bromoiodide emulsion,
2) the proportion of fast emulsion grains in the blend wherein said at
least one slow emulsion is a pure bromide emulsion is less than 40% and
3) the proportion of slow emulsion grains in the blend is greater than 20%
based on the total grain number in said blend.
2. Photographic product according to claim 1, in which the proportion of
fast emulsion is less than 20% based on the total grain number in said
blend.
3. The product of claim 3 wherein said monodisperse silver halide emulsions
have a coefficient of variation of less than 25%.
4. Photographic product of claim 3 wherein the difference in speed between
any two emulsions of the blend having the nearest sensitivities is within
the range of from about 0.2 to about 1 log E.
5. Photographic product according to claim 1, in which the distribution of
silver halides in the bromoiodide emulsion is homogeneous.
6. Photographic product according to claim 1, comprising
16% of fast bromoiodide emulsion containing 3% molar iodide, and
84% slow pure bromide emulsion.
7. Photographic product according to claim 1, comprising:
34% fast bromoiodide emulsion containing 3% molar iodide, and
66% slow pure bromide emulsion.
8. Photographic product according to claim 1, comprising:
15% fast bromoiodide emulsion containing 6% molar iodide,
55% medium bromoiodide emulsion containing 3% molar iodide, and
30% slow pure bromide emulsion.
9. Photographic product according to claim 1, comprising:
15% fast bromoiodide emulsion containing 6% molar iodide,
45% medium bromoiodide emulsion containing 3% molar iodide, and
40% slow pure bromide emulsion.
10. Photographic product according to claim 1, comprising:
10% fast bromoiodide emulsion containing 6% molar iodide,
30% medium bromoiodide emulsion containing 6% molar iodide, and
60% slow pure bromide emulsion.
11. Photographic product according to claim 1, comprising:
10% fast bromoiodide emulsion containing 6% molar iodide,
40% medium bromoiodide emulsion containing 6% molar iodide, and
50% slow pure bromide emulsion.
12. Photographic product according to claim 1, comprising:
10% fast bromoiodide emulsion containing 6% molar iodide,
20% medium bromoiodide emulsion containing 6% molar iodide, and
70% slow pure bromide emulsion.
13. Photographic product according to claim 1, comprising:
5% fast bromoiodide emulsion containing 6% molar iodide,
10% medium bromoiodide emulsion containing 3% molar iodide, and
85% slow pure bromide emulsion.
14. Photographic product according to claim 1, comprising:
10% fast bromoiodide emulsion containing 6% molar iodide,
10% medium bromoiodide emulsion containing 3% molar iodide, and
80% slow pure bromide emulsion.
15. Photographic product according to claim 1, comprising:
10% fast bromoiodide emulsion containing 6% molar iodide,
10% medium bromoiodide emulsion containing 6% molar iodide, and
80% slow pure bromide emulsion.
16. Photographic product according to claim 1, comprising:
15% fast pure bromide emulsion,
45% medium bromoiodide emulsion containing 3% molar iodide, and
40% slow pure bromide emulsion.
17. Photographic product according to claim 1, comprising:
15% fast bromoiodide emulsion containing 6% molar iodide,
55% medium pure bromide emulsion, and
30% slow bromoiodide emulsion containing 3% molar iodide.
18. Photographic product according to claim 1, comprising:
15% fast bromoiodide emulsion containing 6% molar iodide,
55% medium pure bromide emulsion, and
30% slow pure bromide emulsion.
19. The photographic product of claim 1 wherein the difference in speed
between any two emulsions of the blend having the nearest sensitivities is
within the range of from about 0.2 to about 1 Log E (E being exposure) and
the extended latitude in the photographic element is achieved without an
appreciable distortion of the shape of the sensitometric curve.
20. Photographic product of claim 1 wherein the mean equivalent diameter of
the grains in each of the emulsions making up the blend is between 0.2 and
1.5 micrometer.
21. The reversal photographic element of claim 1 wherein the iodide content
of said bromoiodide emulsion is between 0.5 and 20 mol %.
22. Photographic product according to claim 1, in which the total
proportion of iodide in the blend of emulsions is between 1 and 6%.
23. The product of claim 1 wherein said at least one fast silver halide
emulsion is a bromoiodide emulsion.
Description
FIELD OF THE INVENTION
The present invention concerns a photographic product comprising at least
one light-sensitive layer consisting of a blend of silver halide
emulsions.
BACKGROUND OF THE INVENTION
Photographic emulsions are sensitive to light because of the presence of
silver halide grains with different sizes, structures or compositions. The
size of the silver halide grains is directly related to the sensitivity of
the photographic emulsion obtained. In fact, the larger the silver halide
grains making up the photographic emulsions, the more sensitive are the
latter.
However, emulsions with large grains have a higher granularity than
fine-grain emulsions. There is therefore a predictable relationship
between photographic sensitivity and granularity. It has been possible to
determine empirically that whenever the sensitivity of an emulsion is
increased twofold, an increase in granularity of 7 to 10 units is
obtained.
Polydisperse emulsions which have a normal grain size distribution curve
offer a good compromise, which enables sensitive emulsions to be obtained
whilst retaining low granularity. Such emulsions can be obtained directly
by precipitating silver halide grains, or by mixing monodisperse emulsions
of different mean sizes. This technique of mixing monodisperse emulsions
enables emulsions to be obtained with a particularly reproducible
polydispersity.
Photographic products comprising at least one blend of photographic
emulsions with different sensitivities are described in the prior art. For
example, U.S. Pat. No. 4,689,292 describes such a light-sensitive
photographic product having high sensitivity and good covering power.
The products described in the aforesaid patent comprise at least one silver
halide emulsion where the size distribution curve for the grains making up
the emulsion has at least two peaks separated by 0.1 to 0.3 .mu.m, that is
to say the photographic emulsion consists of at least two populations of
silver halide grains having mean grain sizes which differ by at least 0.1
.mu.m and no more than 0.3 .mu.m. These emulsions are spectrally
sensitized by particular spectral dyes affording sensitization of the
orthochromatic type. This emulsion may be obtained from polydisperse
and/or monodisperse emulsions. This emulsion may be utilized in a single
layer or in different superimposed layers. In the examples illustrating
U.S. Pat. No. 4,689,292, the emulsions used are obtained from blends of
polydisperse and/or monodisperse emulsions with a core and a shell,
referred to as "core-shell emulsions", containing at least 20% iodide in
the core. The emulsions obtained have improved speed and better resistance
to pressure, and the photographic products comprising this blend of
photographic emulsions are preferably used in medical radiography.
European Patent Application 83239 describes a color photographic product
formed by several layers of light-sensitive photographic emulsions. These
sensitive layers are such that at least 80% of the total number of silver
halide grains in the product have a mean grain size larger than 0.8 .mu.m
or smaller than 0.65 .mu.m. These silver halide grains of different sizes
may be situated in the same photographic layer or in different layers. The
emulsions used are polydisperse emulsions or blends of monodisperse
emulsions with different mean grain diameters. In the description in this
European patent application, it is mentioned that the composition of the
silver halide grains constituting the blends does not represent a limiting
factor in the invention. However, the emulsions of the blend which are
preferred and described in the examples have identical compositions and
are formed by silver bromoiodide grains containing 4% iodide. In the
examples described in Tables 1 and 3, it can be seen clearly that the
photographic emulsions, in which at least 80% of the total number of
silver halide grains have a mean grain size larger than 0.8 .mu.m or
smaller than 0.65 .mu.m, have improved sharpness and granularity compared
with a polydisperse emulsion comprising a distribution of grain sizes
outside the range claimed. However, the speed of each of the blends of
emulsions of the invention lies between the speed of the most sensitive
emulsion and the sensitivity of the least sensitive emulsion.
European Patent Application 63962 describes a color photographic product
comprising one or more layers of silver halide emulsions formed by at
least two monodisperse emulsions having mean grain sizes of between 0.2
and 3.0 .mu.m. The size distribution curve for the silver halide grains
has two peaks separated by at least 0.3 .mu.m. The silver halide
photographic product obtained is a high-speed photographic product having
improved granularity. The mean size of the grains in the monodisperse
emulsions used is preferably between 0.5 and 1.4 .mu.m. The grains
constituting the monodisperse emulsion or emulsions in the patent EP 63962
may consist of one or more silver halides. However, it is preferred to use
silver bromoiodide or bromochloride grains in which the silver bromide is
the main constituent of the silver halide grains. In the examples, the
emulsions used are silver bromoiodide emulsions containing 2% silver
iodide.
The monodisperse emulsions described above may be used in different layers
or in a blend in one and the same layer. In Table 1 in EP 63962, it can be
seen clearly that the granularity of a blend of emulsions with tabular
monodisperse bromoiodide grains is improved compared with the granularity
of the control emulsion, which in this case is a polydisperse bromoiodide
emulsion with tabular grains.
U.S. Pat. No. 3,989,527 describes a photographic product comprising at
least one radiation-sensitive layer. This radiation-sensitive layer
contains silver halide grains which are surface-sensitized by a spectral
sensitizer. These grains are intimately mixed with silver halide grains
with a mean grain diameter of between 0.15 and 0.5 .mu.m and which are not
spectrally sensitized. These grains which are not spectrally sensitized
enable the exposure radiation to be reflected. These grains, known as
"reflecting grains", represent at least 1% by weight of the total silver
halide grains. The reflecting grains preferably form a monodisperse
population. Their size will be chosen as a function of the wavelength of
the exposure radiation. These emulsions, consisting of spectrally
sensitized silver halide grains and reflecting grains, offer an increase
in speed without degradation of the granularity. In the examples in the
patent, the reflecting grains are monodisperse pure bromide grains (0.48
.mu.m) with a cubic structure. These grains, which are neither chemically
nor spectrally sensitized, are insensitive to the exposure radiation of
the product.
U.S. Pat. No. 4,865,964 describes a photographic product comprising a blend
of bromide or bromoiodide emulsions having tabular grains with a high
aspect ratio and bromide or bromoiodide emulsions having tabular grains
with a low aspect ratio. This blend of emulsions makes it possible to
obtain an advantage with regard to speed and granularity when the
photographic speeds of each of the emulsions making up the blend are
relatively close together.
As is shown by the prior art described above, the blends of emulsions are
often used for improving the sensitometric properties of photographic
emulsions. Indeed, the granularity of a blend of emulsions can be reduced
in a predictable manner by substituting, for some of the coarse grains
making up the blend, grains of smaller sizes, since the granularity of a
photographic image is directly related to the size of the silver halide
grains in the emulsion. In such case, the speed of the blend is between
the speed of the slow emulsion and the speed of the fast emulsion.
In addition, it is known that the speed of a photographic emulsion can be
increased by increasing the size of the silver halide grains, which
necessarily increases the granularity.
In all the patents described above, the blends of emulsions are obtained
from monodisperse silver halide emulsions with different sensitivities,
without any particular conditions with regard to the silver halide
composition of these emulsions.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a continuing need to form photographic elements that have
increased sensitivity without also having increased grain.
SUMMARY OF THE INVENTION
The photographic product of the invention comprises at least one sensitive
layer formed by a blend of monodisperse silver halide emulsions comprising
at least one fast emulsion and at least one slow emulsion, and it is
characterised in that
(1) at least one emulsion making up the blend is a pure bromide emulsion,
(2) the proportion of fast emulsion grains in the blend is less than 50%
based on the total number of silver halide grains, and
(3) the proportion of slow emulsion grains in the blend is greater than
20%.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides a photographic element having improved sensitivity
while also having a low grain. The present invention makes it possible to
obtain a radiation-sensitive photographic product which has improved speed
and granularity. The present invention offers a means for producing a
photographic product having a predetermined sensitometric curve.
DETAILED DESCRIPTION OF THE INVENTION
In the remainder of the description, the term "fast emulsion" designates
the emulsion in the blend which has the highest speed, and the term "slow
emulsion" designates the emulsion in the blend which has the lowest speed.
According to the present invention, the use of a pure bromide emulsion in a
blend of several emulsions makes it possible to increase the speed of the
blend in a surprising manner. Indeed, such blends have a sensitivity very
close to the fast emulsion in the blend, even when the proportion of the
fast emulsion in the blend is as small as 5%. Moreover, this increase in
the sensitivity of the blend is obtained without degrading the
granularity.
The blend of emulsions may contain, in addition to a slow emulsion and a
fast emulsion, one or more emulsions having speeds lying between the speed
of the fast emulsion and the speed of the slow emulsion as defined above
and which make up the blend. In the remainder of the description, these
emulsions will be referred to as "medium emulsions".
The difference in speed between any two emulsions of the blend having the
nearest sensitivities is preferably such that extended latitude in the
photographic element is achieved without an appreciable distortion of the
shape of the sensitometric curve. This difference in speed should be
within the range of from about 0.2 to about 1 Log E (E being exposure).
In the two types of emulsion blend described above (a blend with two
constituents or a blend with more than two constituents), the proportion
of grains of the fastest emulsion is smaller than the proportion of grains
of the slowest emulsion. More particularly, with a blend with two
emulsions, the proportion of grains of the fast emulsion is less than 40%.
With a blend comprising more than two emulsions, the proportion of grains
of the fast emulsion is less than 20%.
According to the invention, the emulsions in the blend are monodisperse
emulsions. The size of these emulsions is determined by volumetric
analysis of the silver halide grains, which is carried out by electrolytic
reduction. Such a method is described by A. Holland and A. Feinerman in J.
Applied Photo. Eng. 8, 165 (1982). This method enables the volume
distribution of the grains to be obtained. From this distribution, it is
possible to calculate, by means of the following formulae, the mean volume
of the grains (V) as well as the equivalent spherical diameter (ESD) and
standard deviation (.sigma.), V.sub.i being the volume of a given grain
and N the number of grains counted.
ESD=2(3V/4.pi.).sup. 1/3 in micrometers
.sigma.=[(.SIGMA.(V.sub.i -V).sup.2 /N)].sup. 1/2
The coefficient of variation (COV) being defined by the formula:
COV=100 .sigma./v
In the present invention, it is preferred to use emulsions with a
coefficient of variation (COV) of less than 25%, and preferably less than
20%.
The mean equivalent diameter of the grains in each of the emulsions making
up the blend is between 0.2 and 1.5 .mu.m. The mean equivalent diameter of
the grains in each of these emulsions will be chosen according to the
desired sensitivity.
In general terms, the sensitivity of an emulsion depends on the size of the
silver halide grains which make it up. However, it is possible, by
optimizing the chemical and/or spectral sensitization of a photographic
emulsion, to obtain an emulsion with a greater sensitivity than an
emulsion consisting of silver halide grains of larger size which has not
been optimally sensitized.
The silver halide grains in the emulsions in the blend other than the pure
bromide emulsion may have different compositions. It is possible, for
example, to use silver bromide, silver iodobromide, silver chloride,
silver chloroiodide or silver chlorobromoiodide grains. The silver halide
grains may be spherical, cubic, octahedral, or cubo-octahedral. When the
emulsions contain several silver halides, the different silver halides may
be distributed in the grains homogeneously or in such a way as to form a
stratiform structure, such as, for example, emulsions with a core and
shell referred to in the remainder of the description as "core/shell
emulsions". These emulsions may also be formed by silver halide grains on
which has been effected an epitaxial deposition of a silver halide
different from the silver halide forming the grains.
According to one embodiment, the emulsions other than the pure bromide
emulsion are bromoiodide emulsions. In the majority of cases, it is
considered that it is possible to use iodide contents of between 0.5 and
20% molar compared with the total silver content, iodide contents of
between 1 and 12% molar compared with the total silver content giving
optimum results in the majority of photographic applications.
The photographic products according to the present invention, when they are
intended for color photography, generally comprise a support having
thereon at least one layer of blue-sensitive silver halide emulsion with
which is associated a yellow dye forming coupler, at least one layer of
green-sensitive silver halide emulsion with which is associated a magenta
dye forming coupler, and at least one layer of red-sensitive silver halide
emulsion with which is associated a cyan dye forming coupler.
These products may contain other layers which are conventional in
photographic products such as spacing layers, filter layers, antihalo
layers, and scavenger layers. The support may be any suitable support used
with photographic products. Conventional supports comprise polymer films,
paper (including paper coated with polymer), glass, and metal. Research
Disclosure, December 1987, No 17643, Section XVII supplies details about
bases and auxiliary layers for photographic products.
The preparation of silver halide emulsions is described, for example, in
Research Disclosure, No 17643, Sections I and II. Silver halide emulsions
may be sensitized chemically in accordance with the methods described in
Section III of the Research Disclosure referred to above. According to the
invention, blends of emulsions may be made up either by mixing
monodisperse emulsions which have been optimally sensitized separately, or
by mixing non-sensitized monodisperse emulsions, sensitization being
effected on the final blend. The chemical sensitizers generally used are
compounds of sulphur and/or selenium and gold. It is also possible to use
sensitization by reduction.
The silver halide emulsions and other layers on the photographic products
of this invention may contain, as a carrier, hydrophilic colloids, used
alone or in combination with other polymeric substances (for example
latices). Suitable hydrophilic substances comprise natural substances such
as proteins, protein derivatives, cellulose derivatives, for example
cellulose esters or gelatin--eg gelatin treated with a base (bovine
gelatin, made from bone or hide) or gelatin treated with an acid (pigskin
gelatin)--gelatin derivatives, for example acetyl gelatin, phthalyl
gelatin, etc, polysaccharides such as dextran, gum arabic, zein, casein,
pectin, collagen derivatives, collodion, agar-agar and albumine.
Spectral sensitization methods, or chromatization, are described in the
same publication, Section IV. The sensitizing dye may be added at various
stages in the preparation of the emulsion, in particular before, during or
after chemical sensitization.
Silver halide emulsions may be sensitized spectrally with dyes from various
classes, including the class of polymethine dyes, which comprises
cyanines, merocyanines, complex cyanines and merocyanines (that is to say
tri-, tetra- and polynuclear cyanines and merocyanines), oxonols,
hemioxonols, styryls, merostyryls and streptocyanines. The above mentioned
Research Disclosure No 17643, Section IV, describes the representative
spectral sensitizing dyes.
The photographic products of the invention may contain, amongst other
things, optical brighteners, anti-fogging compounds, surfactants,
plasticizing agents, lubricants, hardeners, stabilizers, and absorbing
and/or scattering agents as described in Sections V, VI, VIII, XI, XII and
XVI of the above-mentioned Research Disclosure.
The methods of adding these different compounds and the methods of coating
and drying are described in Sections XIV and XV.
According to the invention, the color photographic products comprise, in a
conventional manner, at least three components which are respectively
blue-, green-, and red-sensitive and which provide respectively the
yellow, magenta and cyan components of the subtractive synthesis of the
color image.
The products of the invention, after being exposed, undergo photographic
treatment comprising silver development of the latent image (black and
white development), and then a reversal, which consists of making the
residual unexposed silver halide grains developable by means of a fogging
exposure or a chemical fogging, and subjecting these fogged silver halide
grains to color development in the presence of a color developer and a
coupler, the latter generally being incorporated in the reversible
product.
The photographic products are then washed, subjected to a bleaching bath
and then a fixing bath, before being processed in a stabilizing bath.
Silver development takes place in the presence of a reducing compound which
enables the exposed silver halide grains to be converted into metallic
silver grains. These compounds are chosen from amongst dihydroxybenzenes
such as hydroquinone, 3-pyrazolidones, aminophenols, etc. These compounds
may be used alone or in a blend. This first bath may, in addition, contain
a stabilizer such as sulphites, a buffer such as carbonates, boric acid,
borates or alkanolamines.
The reversal stage is usually effected chemically, either by passing
through a fogging bath containing a reducer, or by introducing the fogging
agent into the color bath. The fogging substances are, for example,
stannous chloride, salts of hydrazine and semicarbazide, ethylenediamine,
sodium borohydride, dimethylborane or thiourea dioxide.
The color developer contained in the color development bath, which enables
the color image to be obtained, is generally an aromatic primary amine
such as the p-phenylenediamines, especially
N,N-dialkyl-p-phenylenediamines, whilst the alkyl radicals and aromatic
ring may be substituted or otherwise. The p-phenylene-diamines used as
chromogenic developers are, for example, N,N-diethyl-p-phenylenediamine
monochlorhydrate, 4-N-N-dimethyl-2-methyl phenylenediamine
monochlorhydrate or 4-(N-ethyl-N-2-hydroxy ethyl)-2-methylphenylenediamine
sulphate. This color development bath may contain other compounds such as
stabilizers, development accelerators, which are generally pyridinium
compounds, or other compounds.
The main compound in the bleaching bath is an oxidizing compound which
transforms the metallic silver into silver ions such as, for example, the
alkaline metal salts of a ferric complex of an aminocarboxyl acid, or
persulphate compounds.
The bleaching compounds normally used are the ferric complexes of
nitrolotriacetic acid, ethylenediamine tetracetic acid,
1,3-propylenediamine tetracetric acid, triethylenetriamine pentacetic
acid, ortho-diamino cyclohexane terracetic acid, ethyliminodiacetic acid,
etc.
The fixing bath enables the silver halide to be totally converted into a
soluble silver complex which is then eliminated from the layers on the
photographic product. The compounds used for the fixing are, for example,
thiosulphates, such as ammonium or alkaline metal thiosulphates.
Stabilizing agents and sequestering agents may be added to the fixing
bath.
The bleaching bath and fixing bath may be replaced with a single
bleaching/fixing bath. The bleaching accelerator compound is generally
present, either in the bleaching bath or in the bleaching/fixing bath. The
processing generally comprises a stabilizing bath containing a color
stabilizer such as formaldehyde, and a wetting agent.
In the following examples, the color reversible photographic products are
exposed and processed in accordance with the standard method for
processing Ektachrome E6.
EXAMPLES
It will be possible to judge the invention and its advantages better by
referring to the following examples:
EXAMPLE 1
In a 20 liter reactor, 4 liters of deionized water and 57.8 g/l of phthalyl
gelatin are introduced. The temperature is raised to 60.degree. C. To this
blend are added an anti-foaming agent and a thioether (I) maturation agent
of the formula:
##STR1##
The pAg of the blend is adjusted to 9 with a NaBr solution and the pH to
5.1 with an HNO.sub.3, 2N solution.
The nucleation of AgBr microcrystals is effected by introducing, by the
double-jet method, a solution of AgNO.sub.3 (0.5M) and a solution of NaBr
(0.5M) for 70 seconds, under agitation at 3500 rpm. An excess of bromide
is kept in the reactor in order to maintain a pAg of 9 at 60.degree. C.
Nucleation is followed by a waiting period of 2 minutes.
A first growth stage of 30 minutes at constant pAg and temperature is then
effected, in which the solutions of AgNO.sub.3 (2M) and NaBr (2M) are
introduced into the reactor in accordance with the accelerated double-jet
method.
This first growth stage enables 3.33 moles of silver halides to be
precipitated.
A second 29 minute growth stage is then effected at constant pAg and
temperature, in which the AgNO.sub.3 (2M) and AgBr (2M) solutions are
introduced into the reactor by the double-jet method at a constant flow
rate of 114.6 ml/min.
In this way a total number of 10 moles of AgBr are obtained. The emulsion
is then washed using the flocculation by salting method in which the pH of
the emulsion is reduced below the isoelectric point (pH 4).
By varying the quantity of the thioether ripening agent introduced into the
reactor before precipitation, the following monodisperse pure bromide
emulsions are obtained:
______________________________________
Thioether
ripening
AgBr agent (mg) ESD (.mu.m)
COV (vol %)
______________________________________
Em (1) 10 0.27 21.1
Em (2) 145 0,64 11
Em (3) 300 1.10 7.7
Em (4) 40 0.37 22.5
______________________________________
EXAMPLE 2
Preparation of bromoiodide emulsions
The bromoiodide emulsions are prepared in accordance with the operating
method described above, except that the two growth stages are effected
from a silver nitrate solution (2M) and a NaBr (2M) solution containing KI
(3% or 6% molar).
By varying the quantity of the thioether ripening agent introduced into the
reactor before precipitation, the following monodisperse bromoiodide
emulsions are obtained:
______________________________________
Thioether
ripening
AgBrI (3 mol %)
agent (mg) ESD (.mu.m)
COV (vol %)
______________________________________
Em (5) 85 0.46 17.2
Em (6) 122 0.55 13.8
Em (7) 300 1.10 8.9
Em (8) 145 0.64 14.1
Em (9) 40 0.37 23.3
Em (10) 122 0.55 12.5
Em (11) 300 1.10 7.9
______________________________________
EXAMPLE 3
Sensitization of the emulsion obtained
The emulsions obtained are optimally sensitized chemically and spectrally.
The emulsions are sensitized chemically with sodium thiosulphate
pentahydrate and potassium tetrachloroaurate, in the presence of sodium
thiocyanate for 20 minutes at 70.degree. C. Then a sensitizing dye of the
following formula is introduced:
##STR2##
EXAMPLE 4
Preparation and processing of the various blends of emulsions
The blends of emulsions are tested in single-layer format.
The blends of emulsions after chemical and spectral sensitization are
coated onto a cellulose triacetate support, with a liter of 0.807
g/m.sup.2 of silver. This layer of emulsion is covered with a surface
coating of gelatin (2.37 g/m.sup.2) containing a tanning agent having the
following formula:
CH.sub.2 =CH--SO.sub.2 --CH.sub.2 13 SO.sub.2 --CH=CH.sub.2
The photographic samples are exposed for 1/100 second using an X20
sensitometer equipped with a lamp with a color temperature of 3000.degree.
K. The sensitometer is equipped with the following filters: one "5A
daylight" filter, "Inconel" filters, and one "Wratten 9" filter.
The samples are exposed through a step tablet comprising 21 incremented
graduations of 0.15 Log E.
The samples are then processed in a standard Ektachrome E6 development
process which comprises the following steps:
Black and white development in a silver halide Solvent
Washing
Reversal bath
Color development (38.degree. C.)
Washing
Bleaching
Fixing
Washing
Stabilization
For each photographic sample, the following characteristics are measured:
the speed in the shoulder for D1 =Dmax-0.3,
the speed D2 for a density of 1, and
the speed in the foot for D3 =Dmin+0.2.
In the following examples, the speeds of the blends of emulsions are
calculated from the speed of the fast emulsion in the blend, to which the
value 100 is allocated.
The granularity is the RMS granularity which takes account of the density
fluctuation. The RMS granularity is measured by means of a granularometer
with a 48 .mu.m exploration hole under the densitometry conditions defined
by the standard ANSI-PH2-19-1976. In the following examples, the
granularity is expressed as a granularity unit variation (.DELTA.GU),
calculated, taking the fast emulsion of the blend as a reference, by means
of the formula:
.DELTA.GU=Log(.sigma.1/.sigma.2)/Log(1.05)
in which .sigma.1 is the RMS of the emulsion or blend of emulsions in
question and .sigma.2 the RMS of the reference emulsion (fast emulsion).
In the following tables, the blends of emulsions are expressed as a
percentage of grains with respect to the total number of silver halide
grains.
Example 4.1 (invention)
In the following table, the fast emulsion is a AgBrI (3%) emulsion and the
slow emulsion is a AgBr emulsion. The blends (I) and (II) are obtained
from Era(8) and Em(4).
TABLE 1
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (8) 100 -- 0 100 100 100 Control
Em (4) 0 -- 100 77 78 90 +1.6
I 34 -- 66 105 107 113 0
II 16 -- 84 105 107 118 0
______________________________________
These results show that the presence of a slow pure bromide emulsion in a
blend of two emulsions results in a surprising increase in sensitivity. In
fact, it can be observed that the speed of the blend is higher than the
speed of the fast emulsion.
Example 4.2 (invention)
In the following table, the fast emulsion is a AgBrI (6%) emulsion, the
medium emulsion is a AgBrI (3%) emulsion and the slow emulsion is a AgBr
emulsion. The blends IV to VII are obtained from Em(11) , Em (6), and
Em(1) .
TABLE 2
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (11)
100 0 0 100 100 100 Control
Em (6) 0 100 0 92 85 81 -16.4
Em (1) 0 0 100 77 78 89 -12.9
IV 15 55 30 104 101 94 -8.4
V 15 45 40 106 100 95 -5.6
VI 10 10 80 103 102 100 -3.2
VII 5 10 85 108 104 101 -4.8
______________________________________
In the following table the fast emulsion and medium emulsion are AgBrI (6%)
emulsions, and the slow emulsion is a AgBr emulsion. The blends IX to XII
are obtained from Em(11), Em(10), and Em(4).
TABLE 3
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (11)
100 0 0 100 100 100 Control
Em (10)
0 100 0 86 76 73 -16.3
Em (4) 0 0 100 81 78 93 -15.7
IX 10 40 50 107 101 91 -10.6
X 10 30 60 108 104 95 -7.5
XI 10 20 70 109 105 96 -4.9
XII 10 10 80 109 110 99 -1.6
______________________________________
In the above examples, a surprising increase in the speed of the blend can
be seen. This increase in sensitivity does not occur to the detriment of
the granularity. It can be seen that this increase in the speed of the
blend is greater for D1 than for D3.
Example 4.3 (invention)
In the following table the fast emulsion is a AgBrI (6%) emulsion, whilst
the medium emulsion and the slow emulsion are AgBr emulsions. The blend
VIII is obtained from Em(11), Em(2), and Em(1).
TABLE 4
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (11)
100 0 0 100 100 100 Control
Em (2) 0 100 0 93 92 115 -8.7
Em (1) 0 0 100 79 74 93 -14.2
VIII 15 55 30 100 100 107 -6.8
______________________________________
In the following table the fast emulsion is a AgBr emulsion, the medium
emulsion is a AgBrI (3%) emulsion and the slow emulsion is a AgBr
emulsion. The blend III is obtained from Em(3), Em(6), and Em(1).
TABLE 5
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (3) 100 0 0 100 100 100 Control
Em (6) 0 100 0 98 86 79 -17.8
Em (1) 0 0 100 84 74 79 -15.2
III 15 45 40 108 106 104 -3.4
______________________________________
It can be seen that the speeds D1, D2, and D3 of the blends described above
are equal to or greater than the values obtained for the fast emulsion.
Example 4.5 (comparison)
In the following table the emulsions are AgBrI (3%) emulsions. The blends
XIII to XV are obtained from Em(7), Era(8), and Em(9).
TABLE 6
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (7) 100 0 0 100 100 100 Control
Em (8) 0 100 0 95 88 91 -14
Em (9) 0 0 100 83 74 88 -21
XIII 33 33 33 97 90 89 -3.2
XIV 25 50 25 100 89 88 -3.9
XV 3 11 85 97 88 86 -8.8
______________________________________
The speeds D1, D2 and D3 for the blends of emulsions which do not contain
pure bromide emulsions are, in all cases, lower than the speeds of the
blends of the invention, even when the proportion of fast emulsion grains
in the blend is as high at 33%.
In the above blends of emulsions, an improvement in granularity is obtained
which is solely due to the replacement of part of a fast emulsion with an
emulsion consisting of silver halide grains with smaller sizes and
therefore of lower sensitivity.
Example 4.6 (invention)
In the following table the fast emulsion is a AgBrI (6%) emulsion, the
medium emulsion is a AgBr emulsion and the slow emulsion is a AgBrI (3%)
emulsion. The blend XVI is obtained from Em(11), Em(2), and Em(5). The
sensitivities obtained are improved compared with the sensitivities
obtained with the bromoiodide blends of Example 4.5.
TABLE 7
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (11)
100 0 0 100 100 100 Control
Em (2) 0 100 0 95 94 109 -7.9
Em (5) 0 0 100 82 72 77 -18.8
XVI 15 55 30 103 97 98 -7.7
______________________________________
Example 4.7 (Comparison)
In the following table, the fast emulsion is a AgBrI (6%) emulsion, the
medium emulsion is a AgBrI (3%) emulsion and the slow emulsion is a AgBr
emulsion. The blend XVII is obtained from Em(11), Em(6), and Era(4).
TABLE 8
______________________________________
Speed
Fast Medium Slow D1 D2 D3 .DELTA.GU
______________________________________
Em (11)
100 0 0 100 100 100 Control
Em (6) 0 100 0 92 82 81 -16.4
Em (4) 0 0 100 77 75 89 -12.9
XVII 10 70 20 100 90 85 -11.2
______________________________________
These results show that the proportion of slow emulsion grains should
preferably be greater than 20%.
The invention has been described in detail with particular reference to
preferred embodiments thereof, but it will be understood that variations
and modifications can be effected within the spirit and scope of the
invention.
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